Testing for No Spark

[Tom Wesenberg]

I just had an email about having no spark, so I'll repeat what I told the man:

Use a test light to see where the voltage stops. With the key off you should have 6 volts on both coil terminals and on the wire from the coil to the switch. With the key on and points closed you should have ground on one side of the coil, both sides of the switch, and both sides of the points contacts. If the test light is lit on one side of the switch but not the other side, then the switch is turned off or it's bad if it's turned on. If the test light is lit on the movable points contact, but not the ground contact, then the points need to be cleaned. If the light is lit on both points contacts, then the distributor needs to be grounded. If the wire is screwed too far into the distributor, then it can ground out the lower plate bus bar.

If the points are open and the key is ON, then you should have voltage all the way to the movable points contact.

[Mike V. Florida]

This is a simple drawing to show the points Tom has mentioned;

[Anteek29]

Mike V. Florida...thanks for posting that handy circuit diagram! I am sticking a copy in my Les Andrews book for future reference.

[pgerhardt]

Thanks Tom and Mike. Here is both the description and diagram in one file for those who want to save and/or print it.

[Mitch//pa]

With the key on points open you should have power all the way to the moveable point contact.

Tom I hope you don't mind that I added that

[Bob Bidonde]

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Tom,
Well done. I have downloaded your post to share with other Model A Ford folks.

[Bruce Adams]

Tom or Mike V.,
Do you have the original drawing showing items 1 to 16 with their explanation?

Could you please post that if you have it?
I was thinking about what to look for on items 15 and 16 to determine if the upper to lower plate wire or contact is broken.
Thanks

[Tom Wesenberg]

Originally Posted by Mitch//pa

With the key on points open you should have power all the way to the moveable point arm.

Tom I hope you don't mind that I added that

Not at all. In fact I will add it to my original posting to make it more complete.

A test light is easier than a multimeter for these checks, and the light bulb puts a small load on the circuit being tested, so it can be a little more reliable in some cases.

It takes almost no current to move the needle on a meter, so a very poor connection can show full voltage, but the bulb will use a little current to make it light up, so if it's dim, you know you have a poor connection.

[Tom Wesenberg]

Originally Posted by Bruce Adams

Tom or Mike V.,
Do you have the original drawing showing items 1 to 16 with their explanation?

Could you please post that if you have it?
I was thinking about what to look for on items 15 and 16 to determine if the upper to lower plate wire or contact is broken.
Thanks

15 is the movable points contact and 16 is the ground points contact.
Key on and no voltage at 15 with points open, then use the test light to follow the circuit and check for an open or ground.

BTW, Harbor Freight has a good test light for under $5.
Don't waste you money on the cheapest test light from the dollar store.

[Flathead]

The test light is an amazing tool. The first step in using a test light is to calibrate it. To calibrate, hook the light across the battery, if it lights you are good to go. If it doesn't light the battery is dead or the light is bad. This is partly in jest, but it is good to verify things before getting in too deep.

[Chuck Sea/Tac]

I've found your diagnoised results are only as good as your test equipment.

[Bruce Adams]

Originally Posted by Flathead

The test light is an amazing tool. The first step in using a test light is to calibrate it. To calibrate, hook the light across the battery, if it lights you are good to go. If it doesn't light the battery is dead or the light is bad. This is partly in jest, but it is good to verify things before getting in too deep.

It kind of works like the redneck weather rope that states if its wet,- its raining, moving- its windy, Hot - its sunny, white - its snowing, stiff -its freezing etc

[Flathead]

Never underestimate the Rednecks!!